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  1. #1

    250X Ultra Running RIVA 9.5:1 Pistons and AUS 98+ BP ULTIMATE

    I have cracked number 3 piston so I bought the following list of parts. I will be running no mods except, anti cavitation mods and the 9.5:1 pistons.

    2 670D1507 RING-O $0.88 $1.76
    1 11061-0090 GASKET,HEAD COVER
    4 11061-3755 GASKET,PLUG HOLE
    1 11061-3708 GASKET,CYLINDER
    1 11061-3742 GASKET,MANIFOLD EXHA
    1 11061-3760 GASKET,MUFFLER
    1 11061-3762 GASKET,PIPE EXHAUST
    1 11061-3716 GASKET,MANIFOLD
    1 11061-3710 GASKET,OIL PAN
    1 92057-3712 CHAIN,98XRH2015-138L
    1 59011-3701 BELT,BANDO RIB-ACE

    1 x RIVA Head Stud Kit, KAW 1.5L Engine (RK10085-HSK)
    1 x RIVA Gasket, Cylinder Head, Std; KAW 1.5L Engine (RK10090-CH)
    1 x KAWASAKI ULTRA 250 ALL PUMP SHOE SEAL KIT (161-25000)
    1 x Ultra 250 Anti-Cavitation Cone (161-25010)
    1 x Solas KX-CD-16/21 Impeller (KX-CD-16/21R)
    1 x RIVA 9.5:1 Compression Ratio Pistons (set of 4) (431-25095)
    1 x KAW. ULTRA 250 DEEP FUEL PICKUP (801-25100)

    With the gear I have to install, is there anything I should be mindful of, it is standard except for the above mentioned parts, I will be running AUS 98+ BP Ultimate at all times.


  2. #2
    MADRUI madrui's Avatar
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    you might expirience some cavitation with the solas prop from what ive being seeing in most of the threads that talk about that prop.
    i was to do what you are going to do, but decide to put the 260 pistons instead.good luck

  3. #3
    nicjak's Avatar
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    and the anticavitation mods are? in my experience a well looked after stock prop and housing will give you zero cavitation tighter the clearance the better the pump will be, thats where any cavitation accurs once its worn a little.wouldnt waste my money on any after market anti cav claims.

  4. #4
    My current prop is stuffed, I probably should have done some more reading on this forum before I purchased the parts. I will give my personal evaluation on the supposed anticavitation mods I have purchased.

    I hope this is not creating a major problem, With the higher compression pistons.
    I have upgraded the head gasket and head studs though.
    Running Standard boost and Stardard everything else.
    With 98+ BP ULTIMATE. Hopefully that is enough octane.

    I want to create a strong motor, I was not happy when I cracked the standard piston.

  5. #5
    nicjak's Avatar
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    why do you think the standard piston cracked?

  6. #6
    I bought the ski with 50hrs on it.
    It could possibly have not been RUN IN properly.
    The bloke I bought it off had a tendency to flog things and not look after them the best.

    The previous owner sucked a rock up through the impeller, I had the impeller fixed by my dealer, and he said it was within tolerances. But by reading on here, it may have had too much gap. The ski was also fully serviced.

    I did have a FI fault where I had to replace a coil pack.

    I do alot of WOT hrs, on a glass lake surface. Spinning 360's etc.
    I take it out into open water.

    The pump also seemed to be cavitating a fair bit, so it was bouncing off the rev limiter at times. (especially when taking off or coming out of a spin)

    The ski was sitting around 8100rpm alot of the time with the 10hrs I done over summer. Probably due to the impeller clearance being to large.

    The ski was using a bit of oil.

    I had to use 98+ BP Ultimate instead of 95+ Premium Unleaded a few times. As the petrol station near where I take the ski out did not have 95+ Premium.

    So nicjak any combination of the above could have contributed, they are all the things I can think of anyway.
    Hence Why I am trying to eliminate as much cavitation as I can and putting stronger pistons in. This will also give me a bit more power.

    Cheers Hunter

  7. #7
    Take the time to smile sirbreaksalot's Avatar
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    Quote Originally Posted by Chykan View Post
    I bought the ski with 50hrs on it.
    It could possibly have not been RUN IN properly.
    The bloke I bought it off had a tendency to flog things and not look after them the best.

    The previous owner sucked a rock up through the impeller, I had the impeller fixed by my dealer, and he said it was within tolerances. But by reading on here, it may have had too much gap. The ski was also fully serviced.

    I did have a FI fault where I had to replace a coil pack.

    I do alot of WOT hrs, on a glass lake surface. Spinning 360's etc.
    I take it out into open water.

    The pump also seemed to be cavitating a fair bit, so it was bouncing off the rev limiter at times. (especially when taking off or coming out of a spin)

    The ski was sitting around 8100rpm alot of the time with the 10hrs I done over summer. Probably due to the impeller clearance being to large.

    The ski was using a bit of oil.

    I had to use 98+ BP Ultimate instead of 95+ Premium Unleaded a few times. As the petrol station near where I take the ski out did not have 95+ Premium.

    So nicjak any combination of the above could have contributed, they are all the things I can think of anyway.
    Hence Why I am trying to eliminate as much cavitation as I can and putting stronger pistons in. This will also give me a bit more power.

    Cheers Hunter
    9.5 pistons and 98 will be fine as long as it maintains 42-43PSI fuel pressure, I have seen OEM pumps and regs slump as low as 38 psi at WOT..........and thats not good , if you know what I mean !!

    Stock timing will be fine , yes you can tweak it but at your own expense

    Waz

  8. #8
    nicjak's Avatar
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    do you really think so waz, sounds like a recipe for disaster if he rides constantly at WOT up and down the beaches doing spins and 360's i would tend to leave it stock to eliminate any chance of destroying it again. 8100rpm seems high for a stock 250, where do you actually ride?

  9. #9
    Thanks Waz

    I ride down in the "Land Down Under, Down Under" Tasmania. Lake Rosebery mostly and Macquarie Heads down Strahan. I have actually been out in 6m seas with it, Ride Beautifully.

    I will be upgrading the Pump and Reg, to ensure it is nearly bomb proof. I also considered Corrilo Rods, But an expense I am not all that willing to spend on this toy, I have a few to many toys to spend money on.

  10. #10
    Quote Originally Posted by nicjak View Post
    do you really think so waz, sounds like a recipe for disaster if he rides constantly at WOT up and down the beaches doing spins and 360's i would tend to leave it stock to eliminate any chance of destroying it again. 8100rpm seems high for a stock 250, where do you actually ride?
    In response. I may have had a slightly bad piston or something, but my riding style definitely needs something stronger than stock. I want it basically stock, but I was always squeezing the throttle wanting more speed or power.

    I was told the 9.5:1 pistons are equivalent to installing a 1:1 pulley with standard 07 pistons. as far as compression in the cylinder. (I will leave it to members on here to confirm this.)

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